156 lines
5.7 KiB
Plaintext
156 lines
5.7 KiB
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From - Mon May 10 15:59:27 1999
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id 10XTfQ-00083Z-00; Wed, 14 Apr 1999 17:41:40 +0000
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Message-ID: <3714B6B6.F745D41D@sferacarta.com>
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Date: Wed, 14 Apr 1999 17:39:34 +0200
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From: Jos<6F> Soares <jose@sferacarta.com>
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To: Thomas Lockhart <lockhart@alumni.caltech.edu>
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CC: hackers <pgsql-hackers@postgresql.org>,
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general <pgsql-general@postgresql.org>
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Subject: Re: [GENERAL] Re: [HACKERS] Gregorian Calendar
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References: <3711B1E5.80213DF6@sferacarta.com> <37135951.88FDB948@alumni.caltech.edu>
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Hi Thomas,
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Thomas Lockhart ha scritto:
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> > I have a question about dates.
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> > The Gregorian reform of calendar skiped 10 days on Oct, 1582.
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> > This reform was accepted by Great Britain and Dominions (including
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> > what is now the USA) only in 1752.
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> > If I insert a date that doesn't exist PostgreSQL accepts it.
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> > Should it be considered normal ?
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>
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> As Peter says, this is tricky.
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>
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> Date conventions before the 19th century make for interesting reading,
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> but are not imho consistant enough to warrant coding into a date/time
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> handler.
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>
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> As you probably have noticed, we use Julian date calculations for our
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> date/time support.
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I suppose you refer to Julian Day invented by the French scholar
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Joseph Justus Scaliger (1540-1609)
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that probably takes its name from the Scaliger's father,
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the Italian scholar Julius Caesar Scaliger (1484-1558).
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Astronomers have used the Julian period to assign a unique number to
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every day since 1 January 4713 BC. This is the so-called Julian Day
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(JD). JD 0 designates the 24 hours from noon UTC on 1 January 4713 BC
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to noon UTC on 2 January 4713 BC.
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Julian Day is different from Julian Date
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The Julian calendar was introduced by Julius Caesar in 45 BC. It was
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in common use until the 1582, when countries started changing to the
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Gregorian calendar.
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In the Julian calendar, the tropical year is approximated as 365 1/4
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days = 365.25 days. This gives an error of 1 day in approximately 128
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and this is why pope Gregory XIII in accordance with instructions
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from the Council of Trent reformed the calendar to correct this error.
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In the Gregorian calendar, the tropical year is approximated as
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365 + 97 / 400 days = 365.2425 days. Thus it takes approximately 3300
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years for the tropical year to shift one day with respect to the
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Gregorian calendar.
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The approximation 365+97/400 is achieved by having 97 leap years
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every 400 years.
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The Gregorian calendar has 97 leap years every 400 years:
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Every year divisible by 4 is a leap year.
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However, every year divisible by 100 is not a leap year.
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However, every year divisible by 400 is a leap year after all.
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So, 1700, 1800, 1900, 2100, and 2200 are not leap years. But 1600,
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2000, and 2400 are leap years.
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instead in the Julian calendar only years divisible by 4 are leap years.
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The papal bull of February 1582 decreed that 10 days should be dropped
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from October 1582 so that 15 October should follow immediately after
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4 October.
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This was observed in Italy, Poland, Portugal, and Spain. Other Catholic
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countries followed shortly after, but Protestant countries were
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reluctant to change, and the Greek orthodox countries didn't change
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until the start of this century.
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The reform was observed by Great Britain and Dominions (including what is
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now the USA)
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in 1752.
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The 2 Sep 1752 was followed by 14 Sep 1752.
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This is why unix has the cal 9 1752 like this:
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September 1752
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S M Tu W Th F S
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1 2 14 15 16
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17 18 19 20 21 22 23
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24 25 26 27 28 29 30
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My question is:
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^^^^^^^^^^^^
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If SQL92 says:
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(Second Informal Review Draft) ISO/IEC 9075:1992, Database
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Language SQL- July 30, 1992
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5.3 literals
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22)Within the definition of a <datetime literal>, the <datetime
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value>s are constrained by the natural rules for dates and
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times
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according to the Gregorian calendar.
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^^^^^^^^^^^^^^^
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Dates between 1752-09-03 and 1752-09-13.
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Are they valid dates?
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^^^^^^^^^^^^^^^^
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> They have the nice property of correctly
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> predicting/calculating any date more recent than something like 4013BC
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> to far into the future, using the assumption that the length of the
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> year is 365.25 days. This is a very recently adopted convention
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> (sometime in the 1800s I had thought, but perhaps it was during the
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> same "reform" in 1752).
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>
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> I've toyed with the idea of implementing a Chinese dynastic calendar,
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> since it seems to be more predictable than historical European
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> calendars.
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People's Republic of China uses the Gregorian calendar
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for civil purposes. Chinese calendar is used for determining
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festivals.
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The beginnings of the Chinese calendar can be traced back to the 14th
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century BC. Legend has it that the Emperor Huangdi invented the
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calendar in 2637 B
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Jos<EFBFBD>
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